


Serpentine

by sparkleshootingstar



Category: IDOLiSH7 (Video Game)
Genre: (of the immortal god/mortal human variety), (of the snake sort), Age Difference, Alternate Universe, Anal Sex, Extremely Dubious Consent, M/M, Riku is a snake god and Tenn is the annual human sacrifice, Unnatural Biology
Language: English
Status: Completed
Published: 2020-04-09
Updated: 2020-04-09
Packaged: 2021-03-02 01:55:03
Rating: Explicit
Warnings: Rape/Non-Con, Underage
Chapters: 1
Words: 3,874
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/23567167
Author URL: https://archiveofourown.org/users/sparkleshootingstar/pseuds/sparkleshootingstar
Summary: Every year, a human sacrifice is sent up to the snake god in the mountains. Tenn had always known that this is how his life would end, but if it's what it takes for their village to stay safe, then he's okay with it.What he didn't expect is for the snake god to haveotherinterests in his body as well.
Relationships: Kujou Ten/Nanase Riku
Comments: 2
Kudos: 65





	Serpentine

**Author's Note:**

  * For [cotton_thistle](https://archiveofourown.org/users/cotton_thistle/gifts).



> PLEASE MIND THE TAGS. There should be a lot more context to this universe, but this fic is really just pure smut (and more than a few shades of problematic). A few things to keep in mind:
> 
> -Riku is a snake god, living at a shrine at the top of a mountain. He used to be accompanied by another god, his brother and "other half," but the other was killed in a human raid over four hundred years ago. Since then, Riku had threatened the village below with devastating plagues and have demanded for them to send an annual human sacrifice. He's hundreds of years old, and looks to be in his mid-twenties.  
> -Tenn is a 16 year old human boy (or is he?) selected to be this year's sacrifice. He'd supposed to take poison within his body and assassinate the ancient god as he's eaten, but that hadn't worked according to plan, and now he's trapped within the shrine.

It’s late afternoon by the time Tenn wakes up from his nap.

Or at least he _thinks_ it’s late afternoon. It’s honestly kind of hard to tell – although the opening of the collapsed cave is enough to allow sunlight through, it’s not very bright, and time had a funny way of blurring together in this quiet, desolate place.

More so since he’d gotten himself chained to Riku’s bed.

Tenn’s lips turn down into a frown as he studies the sturdy iron clasp around his ankle. The chains clank noisily as he pulls on them, but they show no sign of giving – even if he had a weapon, he wouldn’t be able to cut through solid iron by himself. 

This isn’t what he’d had in mind at all when he chose to be confined here. His assigned room had been isolated near the edge of the shrine, and no one came to see him except that fox spirit, Tsumugi, when she brought his meals. When Riku gave him the ultimatum of choosing a location to be chained down to, he’d chosen Riku’s room in hopes of being able to observe the ancient god a little more, maybe to speak with him and learn something useful so he can get word back to Kujou-san – but as it turns out, Riku doesn’t spend much time here during the day. He’ll come back at night, but often at such late hours that Tenn had already fallen asleep waiting – not to mention that Riku almost never even slept in his own bed anyways. 

In fact, he didn’t seem to like sleeping in his human form at all. On the first night, Tenn had watched from the doorway as Riku turned into a tiny black snake and disappeared into the gapes of the gigantic skeleton that laid half-buried across the far side of the cave.

It was a pitiful sight. From what little Riku had spoken of his past, it’s clear that he missed his brother – his other half. The way he’d coop himself up in its skull every night, the raw _grief_ on his face every time he looked upon the skeleton...those things cannot be faked. It’s almost enough to make Tenn feel sorry for him.

In those moments, he’d stop and remind himself of Kujou-san’s words.

 _There’s no need of sympathy for a malevolent god who rules through fear and tyranny. Do your duty, and we will finally be free_.

That’s right. Grief is no excuse for how Riku had cursed the village for over four hundred years, holding the threat of plague over everyone’s heads while demanding annual sacrifices. Not to mention that aside from those brief moments of vulnerability, Riku is absolutely _insufferable_ the rest of the time. He doesn’t understand humans, and has no desire to learn more about them.

The village would be better off without him. 

A splashing sound from the underground lake gives him pause. Sitting up, Tenn swings his legs over the side of the bed and pads to the edge of the room, peering around the corner. Given Riku’s tendency to be absent during the day, he’s pleasantly surprised to see the snake god here this time – that feeling is short-lived, though, when he realizes _why_ Riku is here.

And Tenn feels his face flush red.

Whirling around, Tenn quickly ducks back into the room with his back to the wall. He should’ve realized when he heard the water, for why else would Riku splash around if not for taking a bath? Yet, he hadn’t been prepared for the sight of Riku’s naked body – his broad shoulders, those droplets of water slid down his muscular back–

Tenn’s already facing away from him, but he claps both hands over his eyes anyways. It’s impossible to see Riku like this and not think of that night, less than a week ago–

_"You’re awfully eager, aren’t you? Be a good boy and open up for me now…that’s it…”_

He’d told himself that it was for the sake of his duty, of course. And it was, except it didn’t take long before Riku’s touches had begun to genuinely feel good, and Tenn’s thoughts of everything after that had gotten a little…

Well.

Riku’s the god of disease, not fertility or anything like that. Isn’t it a little unfair for his venom to double as an aphrodisiac? 

Tenn blushes harder at the memory, feeling the heat radiate from his face. There’s no denying his curiosity though, especially since he’d been too out of it to get a good look last time. Unable to help himself, he inches to the edge of the door and peeks around it again. 

If Riku notices Tenn, he doesn’t show it. Slowly, languidly, he stretches like a lazy cat and pulls himself up to sit in the shallows. The trail of water guides Tenn’s gaze as it drips down Riku’s bare torso, water dripping down to his navel, the shape of his pelvis and–

 _Oh_.

Tenn clasps both hands over his mouth, but that doesn’t entirely muffle the strangled gasp slipping from his lips.

Did Riku always have… _two_ …?

It hadn’t been like this when they slept together! At least, Tenn didn’t think it was – again, it had been too dark (and honestly, too overwhelming) for him to pay attention, but he’s fairly sure that he’d only felt one… _one_ of those things, penetrating him.

Surely it was only one. At _that_ size, there’s no way having two would fit.

Right?

With a full-body shiver and a shake of his head, Tenn whirls back around and sinks to his knees behind the door. Riku’s a god, so it isn’t a question of _how_ or _why_ his biology is different in that way, but…isn’t this too much? Riku had fucked him once already and he’d been so _big_ – if that was just one, what had he been doing with the second? Tenn knows he’d passed out halfway through, so could Riku have– oh _god_ –

His face must be on fire now. Tenn curls in a little tighter in on himself as he frantically tries to backtrack on that train of thought.

He doesn’t dare look again. Moving slowly so as not to rustle the chains, Tenn tip-toes back to the bed and dives under the covers. He should just…ignore Riku for now. It’s not like Riku would be up for talking while he’s taking a bath, anyways, so he won’t learn anything useful. 

And yet–

There’s heat coiling at the pit of his stomach, an odd ache at his groin, and Tenn’s breathing turns ragged as he starts to rub his thighs together. Even when he closes his eyes, the image stands out clear as day.

_“I’ll be gentle with you tonight, so relax.”_

That’s what Riku had said during their first night together, yet the experience had been so overwhelming that it made Tenn breathless just thinking about it. Riku had fucked him unconscious that time and he’d woken up the next morning sore and unable to walk, cursing the snake god for being a horny, inconsiderate bastard. But if Riku had _two_ , then…

…Had he been going easy on him, after all? 

Regardless, is it even possible to fit both inside? Even with one, he’d been so full that it felt as though he might tear at the seams. If Riku used both, surely it would _ruin_ him. His insides would be wrecked, rearranged–

Without realizing it, Tenn’s hand had slipped past the folds of his yukata to palm at his own hardening member. It’s only when a soft moan slips past his lips that he realizes what he’s doing and abruptly snatches his hand back with a start.

_No, no, no–_

Watching was bad enough. He won’t sink to touching himself to thoughts of Riku! Panting heavily, Tenn presses his legs close together and curls in on himself a little more, willing for the shameful erection to fade.

He doesn’t even notice the approaching footsteps until a shadow falls over him.

“What’s got you thinking so hard, brat?”

Tenn’s entire body goes stiff. For a moment, he doesn’t even dare move as he remains curled up on his side, facing away from Riku even as sheer panic builds up within his chest. Somehow, he’d gotten so worked up that he hadn’t even heard Riku walking up to him.

_Maybe, if I pretend to be asleep…?_

Unfortunately, his lack of an answer doesn’t seem to deter Riku at all. “I know you’re awake. Bit late for you to still be in bed, isn’t it?”

Tenn takes a deep breath and a moment to compose himself, the rolls over to his other side, making sure to keep himself carefully concealed under the blankets. “Am I not allowed, Riku-sama?” he struggles to keep his expression neutral. “It’s not like I can leave.”

“ _You_ were the one who chose to be chained up here.”

“You forced me to choose!” 

“Because you kept running off,” Riku raises an eyebrow. “And frankly, I don’t have the patience to keep an eye on you all the time. It’s much easier this way.”

“Then it doesn’t matter if I stay in bed all day,” Tenn doesn’t mean to sound so petulant, but he can’t concentrate when so painfully aware of his erection. He curls in on himself, self-consciously drawing the blankets closer. “There’s nothing to do, anyways.”

He realizes his mistake a moment later when Riku smirks, slow and deliberate, and sits down beside him on the bed.

“Nothing to do? Really?” Riku places his hand over the blanket, just over Tenn’s hip. “I find that hard to believe.”

Then, before Tenn can stop him, he tightens his grip on the fabric and pulls at it _hard_.

“Don’t–!”

Tenn tries to hold onto the blanket, but it’s too late. It slides right out of his hands as Riku drags it off and throws it over the side of the bed, exposing the tent in his yukata for them both to see. When Tenn instinctively tries to cover himself, Riku snatches up both of his wrists, effortlessly pinning them over his head with a single hand. 

He’s looming over him now, lips pulled back into a wide enough grin for Tenn to see his fangs. Slowly, Riku leans down, his breath hot against Tenn’s ear.

“I heard you, you know.”

Tenn holds perfectly still. He doesn’t even dare breathe.

“You saw, right?”

“N-No–“

Tenn’s words cut off into a startled squeak as Riku’s tongue darts out, flicking light and wet against his neck. “Bad boy,” he breathes, voice lowering to a husky whisper. “Don’t lie.”

“…I…I’m sorry, Riku-sama.”

It’s humiliating how, even now, he’s still painfully hard. Tenn sucks in a few more ragged breaths, pressing his legs close together to try and hide it. It’s to no avail as mere moments later, he feels his thighs being nudged apart when Riku moves his knee in between.

_No more, please, leave me be–_

But of course, Riku doesn’t do any of that. “So did you like what you saw?” he continues, almost purring. A hand trails down Tenn’s side, sliding inside his half-open yukata to grope lightly at his waist before trailing further down. “Perhaps I didn’t need to ask, considering your current state.”

Tenn shakes his head, his entire body trembling. “No, don’t…”

“Tell me what you want,” Riku nuzzles against his cheek. “I’ll give it to you if you ask nicely.”

And it’s that mocking, _patronizing_ tone that finally gives Tenn the burst of determination to open his eyes and glare. “I don’t want it…!”

Riku pauses. He pulls back, just slightly, and Tenn’s heart stutters for a moment – only for his hopes to quickly be dashed as Riku uses his other hand to push his thighs further apart, pulling the already-loose tie of his yukata open and fully exposing his erection.

“You don’t want me to touch you?” 

“N-No!”

“Even though you’re so worked up?” Riku offers a sickly sweet smile, his grip tightening over Tenn’s wrists as he pushes his legs further apart and brushing dangerously close to his member. “Then…show me how you were going to deal with this.”

Once he gets over his shock, Tenn immediately tries to kick him. “Let go–!”

“But look at how wet you are already,” Riku continues. His blood-red eyes glint with malicious amusement. “Just from watching me bathe?”

“I didn’t mean t–”

“You’re _leaking_ ,” Riku continues ruthlessly. He makes no move to touch Tenn, yet the look in his eyes is so intense that it sends shivers through Tenn. “I’ve only fucked you once, and you’ve already become a sexual deviant. Weren’t you a virgin when you came up here?”

“Stop,” Tenn’s chest heaves with shallow, panicked breaths. “Don’t–”

“And yet that very first night had you moaning like a whore. I wonder if the Kujous sent me the wrong person by accident – it’s just hard to imagine that you were ever pure, you know?”

The times, tears of frustration and humiliation spring to Tenn’s eyes. It takes everything he has not to let them fall. Riku’s jabs are taunting, borderline _cruel_ , and the worst part is that he isn’t wrong at all. Tenn’s behaviour that night had been obscene. Shameful.

And even now, when held down and degraded, his arousal isn’t going away.

“In that case, I’ll help you.”

Letting out a teary whimper, and Tenn closes his eyes as Riku loosens his grip on his wrists, taking one of his hands and leading it down until his fingers are wrapped around his own length. With his hand over Tenn’s own, Riku slowly begins to move, coaxing Tenn to stroke up and down his cock with lubrication from his own precum. 

“Ah…ah, ngh…!”

“See?” Riku’s voice is barely a whisper. “It feels good, doesn’t it? You’re at that age after all.”

Tenn writhes under him, small, choked moans and whines leaking out even as he bit down hard on his bottom lip.

“None of that, now,” Riku nuzzles him again. He’s so, so close. “Let me hear you.”

He claims Tenn’s lips with his own, swallowing the startled gasp that escapes and plunging into Tenn’s mouth before the younger can react. Tenn can feel Riku’s tongue licking into his mouth, longer and more flexible than a human’s should be – yet he doesn’t feel disgusted at all, can barely conjure up a coherent thought as a new wave of heat floods through him.

When Riku pulls back, Tenn instinctively finds himself arching up for more. Riku laughs and pushes him down again, releasing his hands.

“Good boy.”

It takes Tenn a moment to realize he’d begun to stroke himself fervently, without any of Riku’s previous coaxing. His body feels as though it’s begun to burn up, the ache in his groin growing unbearably strong – and now, even when Riku has let go, even when he’s just _watching_ now with those smug, lecherous eyes, he can’t stop. Helpless tears spill down his cheeks as he arches up again, letting out choked, wanton moans.

This isn’t enough. He feels so _empty_.

“P…Please… _p-please_ …”

“Please what?”

Tenn gives him a desperate look, arching up again in hopes of obtaining some sort of friction. However, Riku doesn’t move. “You’re going to have to be more specific than that.”

He’s not going to make him say it out loud, is he? Tenn’s right hand hadn’t stopped moving, but he reaches for Riku with his left, hoping to show him instead – only for Riku to catch his wrists again. Tenn lets out a frustrated cry as they’re pinned back above his head, denying him even the touch that he’d been granting himself.

“I didn’t give you permission to touch me,” Riku says. “I want you to _say_ it. If you insist on being stubborn, I may run out of patience.”

“N-No…no…”

“Should I tie you up like this and leave you here?”

“No!” Tenn finally bursts out, his chest heaving on the edge of a desperate sob. He’s so hot all over – if Riku leaves him like this, unable to touch himself, he thinks he might actually go insane. “Don’t leave, please don’t leave, I– I just–” more tears spill down, dripping freely down his cheeks. “I want your cock in me!”

Having those words spoken out loud is almost too much. Tenn dissolves into soft sobs after that, his entire body trembling and cock still leaking, shamefully on display between them. Riku’s expression, however, softens slightly. He lets go off Tenn’s wrists again, and finally raises a hand to wipe the tears from his face.

“Maybe I went too far,” he murmurs, and Tenn gives a gasp as Riku’s other hand finally trails downwards, wrapping around him firmly. With one finger, he teases the slit. “But you were finally honest. Good boy.”

“Riku-sama,” Tenn whimpers, hips buckling into each stroke. “Please, _please_ …”

“Since you asked, I’ll give you what you want,” Riku draws back slightly, just long enough to pull off his loose robe and tossing it to the side. He’s hard, too, and Tenn swallows dryly upon seeing _both_ of Riku’s erections, thick and heavy and already leaking precum from the tips. 

He’s too turned on to say no regardless, but would it even fit? God, just one would be enough to turn him inside out…what if Riku wanted to…?

Riku must’ve seen the look on his face, because he barks out a short laugh even as he sets about to spread Tenn’s legs, pressing against the rim of his hole with a finger. “No, I’m not going to fuck you with both.” He pauses. “Maybe.”

Tenn blanches. “Maybe–?!”

The rest of the sentence cuts off as Riku lines himself up and thrusts into the hilt. He hadn’t prepared him properly and it _hurts_ as he’s stretched wide and open to make room for Riku’s cock, but the pain fades almost as quickly as it comes as Riku bottoms out with a pleased sigh, rocking his hips against Tenn’s from where they’re joined.

Without even thinking about it, Tenn reaches forward to wrap his arms around Riku’s neck, clinging on as close as possible. He feels hot all over, and the unbearable heat only seems to get worse the more Riku touches him – in the back of his mind, he realizes that this must be the work of the aphrodisiac in Riku’s bodily fluids, just like what had happened that first night they’d slept together, but he also can’t bring himself to care right at that moment.

“Riku-sama…”

It’s so warm like this. He feels almost loved.

Riku nuzzles at his cheek, the gesture surprisingly affectionate as he begins to draw back slightly before thrusting forward again, setting a steady rhythm. Tenn’s mouth falls open and each time Riku moves, it fucks small, breathless moans out of him.

All strength seems to have bled out of his body, leaving him boneless and soft, but Tenn continues to cling on as hard as he can, wrapping his legs around Riku from the back and trying his best to meet every thrust. “More, more–” 

“I took it easy on you the first time,” Riku whispers in his ear. “But you can do it this time, right? Is it good?”

“It’s so good,” Tenn chokes out. More tears spill down his cheeks, his chest heaving with every breath. “Riku-sama, harder _–_ ”

His voice tilts into a scream as Riku slams into him again, hitting so hard and deep that Tenn swears he can feel the shape of Riku’s cock through his stomach. 

“Ask nicely.”

“Please!” Tenn sobs, his body wracked by little spasms between pain and pleasure as Riku slams up against his prostate again and again. “ _Please_ , Riku-sama!”

Riku doesn’t say anything, but his fingers dig into Tenn’s hips as he begins to move faster, harder, pushing Tenn down on the mattress each time he moves. A particularly hard shove has Tenn screaming, his eyes rolling up. Riku’s grip on him doesn’t loosen, though, and his thrust fills him up so completely that Tenn’s wailing as he comes, clenching hard around Riku’s cock as he spills all over his own stomach.

But Riku doesn’t stop. He fucks Tenn through his orgasm, not even slowing down when Tenn finally comes down from his high and begins to cry from all the overstimulation.

“Riku-sama, s-stop…”

“I won’t,” Riku’s panting now, too. “Since you asked for it, you better take it all.”

Tenn writhes beneath him, sobbing, but remains steadily trapped under his body weight. Even as the overwhelming ache from before was fading ever so slightly, Riku’s steady movements stirred up a new coil of heat in his gut. There’s a lewd, slapping sound every time their hips meet, and Tenn chokes on each heaving breath as drool leaks out the side of his mouth.

There’s so much. He’s so sensitive inside it feels as though Riku must be tearing him apart, every bit of him so exhausted that he can’t even keep his arms around Riku’s shoulders anymore. Yet through it all, Tenn can feel himself becoming hard again.

“I can’t, _I can’t–_ ”

He screams when Riku thrusts one last time and _grinds_ into him instead of pulling back. There’s a flood of warmth, filling him up – but it doesn’t stop like Tenn expects after a while, and it just _keeps going_ even when he starts to feel pressure on his abdomen.

“T…T-Too much…” 

“It’s okay,” Riku coaxes, bending to flick his tongue against Tenn’s ear. "See how well you’re taking it?”

“I can’t!” Tenn gasps, shaking his head. He feels almost delirious now, his vision blurring as he struggles to concentrate. “Riku-sama, no…no more…”

He’s crying softly when it finally stops. When Riku pulls out, Tenn feels a gush of wetness between his legs as the cum begins to leak from him almost immediately. Even when he clenches, his worn-out muscles refuse to cooperate. 

Then, abruptly, he finds himself being flipped over. Tenn gives a startled squeak, grimacing at the feeling of the wet and sticky puddle pressing against his stomach instead as Riku pushes his legs open again. His heart almost stops when he feels something hard pushing against his gaping entrance.

“Stop–”

He’s so wet and loose inside that there’s no resistance at all – Riku bottoms out on the first thrust, and Tenn cries out feebly as he’s filled again. Somehow, Riku’s still hard – and with how much aphrodisiac is in his system, it doesn’t take long before Tenn’s own cock is hardening again. Even though he’s exhausted, without even enough energy to raise his head, he finds himself rocking his hips back to meet each of Riku’s movements.

How is Riku still going? Doesn’t he tire at all?

How long until a god’s libido is satisfied?

“N-No more…no more, Riku-sama…” Tenn’s voice cracks. “I-I’m going to break…!”

There’s a low, husky laugh from behind him, as Riku nuzzles into the back of his neck, his pace never slowing.

“I won’t break my toys so quickly, Tenn. Just lay back...” A sharp nip, just barely enough to break the skin. “And let me take care of you.”

**Author's Note:**

> For [cotton_thistle's](https://archiveofourown.org/users/cotton_thistle/works) birthday. She wanted this very specific smut, and I delivered because, well, what else are friends for? 
> 
> Don't think too hard about it, though comments are always welcome.


End file.
